SITU-MON is a machine-language monitor for MOS 6502-based microcomputer systems. (This item emulates it under a Commodore 64).
It was coded by hand on paper, then entered into an emulated Commodore 64 using SITU-PAN in the Bootstrap Zero project during RetroChallenge 2015/07. In turn, it was used to enter SITU-SOL, a minimal compiler for a minimal FORTH-like language.
To start the monitor once loaded, execute SYS 33024.
For documentation and (non-machine-readable) source code for SITU-MON, see the Bootstrap Zero item.